In recent years, the increasingly high density of electrical circuits in the field of electricity and electronics has been accompanied by a shift towards finer linewidths and narrower spaces between lines. However, as spaces between lines become narrower, shorts between lines and electromigration tend to arise.
The following circuit board production method is disclosed in Patent Document 1 as art capable of addressing this problem. First, a resin film is formed on the surface of an insulating substrate (resin film forming step). Next, a circuit pattern is created by forming recessed portions having a depth, with reference to an outer of the resin film, which is equal to or greater than the thickness of the resin film (circuit forming step). Then a plating catalyst or a precursor thereof is deposited on the surface of the circuit pattern and the surface of the resin film (catalyst deposition step). Next, the resin film is removed from the insulating substrate (film removal step). An electroless plating film is then formed only in areas where the plating catalyst or precursor thereof remains behind following removal of the resin film (plating treatment step). Such a production method makes it possible to form highly accurate electrical circuits on an insulating substrate, enabling a circuit board in which the occurrence of short circuits and electromigration is suppressed to be obtained.
In the foregoing production method, Patent Document 1 mentions laser processing as one method of forming the circuit pattern. In addition, Patent Document 1 states that the productivity is improved by using a resin film having a high absorbance at the characteristic wavelength of the laser light. However, specific art for increasing the absorbance of laser light by the resin film is not mentioned.    Patent Document 1: Japanese Patent Application Laid-open No. 2010-135768 (paragraphs 0018, 0100 and 0102)